Repeater and optical communication system

ABSTRACT

Disclosed is a repeater including: a recognizing unit to recognize a destination address of an optical packet from the optical packet which includes the destination address assigned in unit of bit and a bit indicating whether or not a plurality of destination addresses are assigned; an optical splitting unit to split the optical packet into a plurality of optical packets; and selecting units to select transmission channels for the split optical packets on the basis of recognition results by the recognizing units, respectively.

FIELD OF THE INVENTION

The present invention relates to a repeater for relaying optical packetsand an optical communication system using the repeater for transmittingoptical packets.

DESCRIPTION OF RELATED ART

Optical communication systems using optical signals for datacommunication have become widely used in recent years. In the opticalcommunication systems, packet communication is performed in a similarway to data communication by using electric signals. (For example, referto Patent document 1: JP-2003-069495A) In data communication, the packetcommunication is communication in which data is divided into a pluralityof small data blocks which are called packets, and the divided datablocks are sent or received.

An operation for switching the optical packets by a conventionalrepeater will be described with reference to FIG. 10. In FIG. 10, anoptical packet P1 is transmitted through an optical transmission channel200 (for example, an optical waveguide such as an optical fiber, and thelike) to a repeater 201. In the repeater 201, a destination address andsource address contained in a header portion of the optical packet P1are referred, and a transmission channel through which the opticalpacket is to be transmitted is selected. For instance, the repeater 201selects an optical transmission channel 205 and outputs an opticalpacket P2 to the following repeater 203 through the optical transmissionchannel 205. A repeater which performs destination control, that is,switches a transmission channel is called a network switch.

FIG. 11 is a view showing a configuration of a conventional repeater.Hereinafter, the repeater 201 connected with the optical transmissionchannels 200, 204 and 205 will be described as an example of aconventional repeater. The repeater 201 comprises optical ports 206, 207and 208, a packet processing unit 209, and a storing unit 210. Thepacket processing unit 209 comprises a CPU (Central Processing Unit) andan ASIC (Application Specific Integrated Circuit). The storing unit 210comprises, for example, an RAM (Random Access Memory) and the like. Theoptical ports 206, 207 and 208 are connected to the optical transmissionchannels 200, 204 and 205, respectively. The packet processing unit 209is connected to the optical ports, and the storing unit 210 is connectedto the packet processing unit 209.

The optical port 206 receives the optical packet P1 through the opticaltransmission channel 200 and converts the optical packet P1 into anelectric signal packet, to output the same to the packet processing unit209. The packet processing unit 209 reads a destination address (and asource address, as need) included in the header portion of the opticalpacket converted into an electric signal to select an optical port forthe destination.

The packet processing unit 209 sometimes transfers the packet to theoptical port for the destination after storing the packet in the storingunit 210, or transfers the packet to the optical port without storingthe packet in the storing unit 210. In the example shown in FIG. 11, thepacket processing unit 209 selects the optical port 208 connected to theoptical transmission channel 205, and transfers the electric signalpacket to the optical port 208. The optical port 208 converts theelectric signal packet into an optical signal packet (optical packet P2)and outputs the optical packet P2 to the optical transmission channel205. In the manner described above, the optical packet is transferred tothe optical transmission channel selected by the repeater.

Referring to FIG. 12, an optical communication system for transferringone optical packet to a plurality of optical transmission channels willbe described. It is possible to perform one-to-many communicationeffectively by reproducing or copying one optical packet andtransferring a plurality of optical packets having the same contents toa plurality of optical transmission channels. It is called “Broadcast”to transfer an optical packet to all connected optical transmissionchannels, and it is called “Multicast” to transfer an optical packetonly to the optical transmission channels selected from among theplurality of optical transmission channels. FIG. 12 is a viewillustrating a case where the optical packet P1 is duplicated or copiedin the repeater 201, and the optical packets P2 and P3 having the samecontents are transferred to the optical transmission channels 205 and204, respectively.

With reference to FIG. 13, an operation in the repeater 201 will bedescribed, which is performed to transfer the optical packet P1 to theoptical transmission channels 204 and 205.

The optical packet P1 is transferred through the optical transmissionchannel 200 to the repeater 201, and converted into an electric signalpacket by the optical port 206, and outputs to the packet processingunit 209. In the packet processing unit 209, an optical port for adestination is selected based on a destination address (and a sourceaddress, as need) contained in the header portion of the packetconverted into an electric signal. The packet converted into an electricsignal is stored in the storing unit 210 and then transferred to theoptical ports 207 and 208 connected to the optical transmission channels204 and 205, respectively.

In the optical port 207, the electric signal packet is converted into anoptical signal packet (optical packet P3), and the optical packet P3 isoutput to the optical transmission channel 204. In the optical port 208,the electric signal packet is converted into an optical signal packet(optical packet P2), and the optical packet P2 is output to the opticaltransmission channel 205. In this way, the optical packet is transferredto a plurality of optical transmission channels by the repeater.

As shown in FIGS. 11 and 13, in the conventional repeater, since thepacket processing unit 209 and storing unit 210 processes the packetelectrically, it is essential to convert an optical signal into anelectric signal and to convert an electric signal into an opticalsignal. Therefore, there are the following problems.

Since a processing speed of an electric process is considerably lowcompared with a speed in an optical communication, a processing delayoccurs while an optical packet or optical signal is converted into anelectric signal of a low speed, and the converted electric signal isprocessed electrically. Therefore, when the optical packet passesthrough a plurality of repeaters, a disadvantage is invited, thatrequires a longer time for the optical packet to pass through aplurality of repeaters, since a processing delay occurs in everyrepeater.

To avoid the above disadvantage, electric circuits and equipment of aconsiderably large scale-are required, which are capable of performingsuch electric processes at a processing speed comparable to that of theoptical communication. Therefore, it is hard to put these circuit andequipment into practical use. Further, in the broadcast transmissionand/or multicast transmission, since a single packet is duplicated intoa plurality of packets in the packet processing unit 209, anotherdisadvantage occurs that increases operation load to be applied to thepacket processing unit 209.

SUMMARY OF THE INVENTION

An object of the invention is to realize an optical communication with ahigh speed without increasing a circuit scale of the repeater.

In order to achieve the above-described object, in accordance with afirst aspect of the invention, the repeater comprises: a recognizingunit to recognize a destination address of an optical packet from theoptical packet which includes the destination address assigned in unitof bit and a bit indicating whether or not a plurality of destinationaddresses are assigned; an optical splitting unit to split the opticalpacket into a plurality of optical packets; and selecting units toselect transmission channels for the split optical packets on the basisof recognition results by the recognizing units, respectively.

Preferably, in the repeater, a plurality of specified addresses can bedesignated for each of the optical packets split by including acombination of bits each indicating a destination address and a bitindicating that a plurality of destination addresses are assigned.

In accordance with a second aspect of the invention, the opticalcommunication system comprises a repeater provided in a network, fortransferring an optical packet, wherein the repeater comprising: arecognizing unit to recognize a destination address of an optical packetfrom the optical packet which includes the destination address assignedin unit of bit and a bit indicating whether or not a plurality ofdestination addresses are assigned; an optical splitting unit to splitthe optical packet into a plurality of optical packets; and selectingunits to select transmission channels for the split optical packets onthe basis of recognition results by the recognizing units, respectively

Preferably, in the optical communication system, the repeater isprovided in a ring type network.

According to the invention, destination addresses are recognized from anoptical packet having a simple address configuration, the optical packetis split by splitting means, and the split optical packets aretransferred respectively to transmission channels corresponding to thedestination addresses, whereby an optical communication is performed ata high speed without electrically processing the optical packet in arepeater nor increasing a circuit scale of the repeater.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be fully understood with reference to thefollowing detailed description and the accompanying drawings. These areonly for explanation of the invention, and by no means restrict thescope of the invention, wherein

FIG. 1 is a view illustrating a flow of an optical packet in thebroadcast transmission,

FIG. 2 is a view illustrating an interior configuration of a repeateraccording to an embodiment of the invention, and a transferringoperation of the optical packet from the repeater to a network andfurther to a following repeater,

FIG. 3 is a view illustrating an operation for breaking off the opticalpacket in the repeater according to the embodiment of the invention,

FIG. 4 is a view illustrating a flow of the optical packet in themulticast transmission,

FIG. 5 is a view showing an address configuration of a header portion ofthe optical packet,

FIG. 6 is a view illustrating a transferring operation for transferringthe optical packet from the repeater to the following repeater,

FIG. 7 is a view showing a duplex ring type network,

FIG. 8 is a view illustrating the duplex ring type network with adisconnection failure occurring in the optical transmission channel,

FIG. 9 is a view showing an operation performed in the repeater when adisconnection failure occurs in the optical transmission channel,

FIG. 10 is a view illustrating a switching operation of an opticalpacket through the repeaters in a conventional optical communicationsystem,

FIG. 11 is a view showing an interior configuration of the conventionalrepeater and an operation performed in the repeater,

FIG. 12 is a view illustrating the broadcast transmission or multicasttransmission of the optical packet by the repeater in the conventionalcommunication system, and

FIG. 13 is a view illustrating an operation performed by theconventional repeater in the broadcast transmission and multicasttransmission.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Now, embodiments of the invention will be described with reference tothe accompanying drawings.

[Broadcast]

Using a ring type network as a sample of a communication network, abroadcast transmission in an optical packet network will be describedwith reference to FIGS. 1 to 3.

FIG. 1 is a view illustrating a configuration of an opticalcommunication system 1S according to an embodiment of the invention, anda flow of optical packets (shown by solid arrows) in the broadcasttransmission. The optical communication system 1S is provided with aplurality of repeaters 1 to 4 on a ring type network 100 as shown inFIG. 1. The repeaters 1 to 4 are connected with networks N1 to N4,respectively. In FIG. 1, the optical communication system 1S which isprovided with four repeaters is illustrated, for simplicity, fordescribing the embodiment of the invention, but there is no limitationto the number of the repeater.

An optical packet generated in the network N1 is transferred through anoptical transmission channel 5 to the repeater 1 and further to the ringtype network 100 therefrom. The optical packet runs on an opticaltransmission channel 6 from the repeater 1 to a repeater 2. Then, theoptical packet is duplicated in the repeater 2, and transferred tooptical transmission channels 7 and 8. The optical packet transferred tothe optical transmission channel 7 reaches the network N2, and meanwhilethe optical packet transferred to the optical transmission channel 8reaches the repeater 3. In the same way, the optical packet isduplicated in the repeater 3 and transferred to optical transmissionchannels 9 and 10. Further, the optical packet transferred to theoptical transmission channel 9 reaches the network N3 and the opticalpacket transferred to the optical transmission channel 10 reaches therepeater 4. Thereafter, the optical packet is duplicated in the repeater4 and transferred to the network N4 through an optical transmissionchannel 11, and also transferred through an optical transmission channel12 to return to the repeater 1, which serves as a gate to the ring typenetwork 100.

The optical packet which has returned to the repeater 1 serving as thegate to the ring type network 100 is broken off in the repeater 1. Ifthe optical packet is not broken off by the repeater 1, the opticalpacket goes around the ring type network 100 again, and keeps goingaround eternally. Therefore, a process of the repeater 1 for breakingoff or removing the optical packet is necessary.

FIG. 2 is a view illustrating an interior configuration of the repeaterprovided in the optical communication system 1S. The interiorconfiguration of the repeater 2 is shown in FIG. 2, and each repeaterprovided in the optical communication system 1S has the sameconfiguration. As shown in FIG. 2, the repeater 2 comprises an addressrecognition circuit 20, optical splitter 21, optical switch 22 andoptical switch 23.

The address recognition circuit 20 recognizes a destination addresscontained in a header portion of the optical packet, and outputs acontrol signal generated based on the recognition result to the opticalswitches 22 and 23. The destination address has a bit which indicateswhether or not the optical packet is transferred to a plurality ofdestinations (broadcast transmission, multicast transmission, unicasttransmission) (refer to FIG. 5).

The optical splitter 21 splits the received optical packet into aplurality of packets (two packets in FIG. 2) to duplicate a plurality ofoptical packets having the same contents. Two optical packets duplicatedby the optical splitter 21 are output to optical switches 22 and 23,respectively.

The optical switches 22 and 23 select transmission channels for theduplicated optical packets on the basis of the destination addressesrecognized by the address recognition circuit 20.

Now, operation will be described, which is performed by the repeater 2in the broadcast transmission.

When the optical packet is entered to the repeater 2, the addressrecognition circuit 20 recognizes that the optical packet has beentransferred in the broadcast transmission. The address recognitioncircuit 20 generates a control signal based on the recognition resultand outputs the control signal to optical switches 22 and 23. Meanwhile,the optical packet entered to the repeater 2 is split by the opticalsplitter 21 and output to the optical switches 22 and 23.

In a case of the broadcast transmission, the optical switch 22 selectsthe optical transmission channel 24, and the optical packet duplicatedby the optical splitter 21 is transferred to the optical transmissionchannel 24. Meanwhile, the optical switch 23 selects the opticaltransmission channel 25, and the duplicated optical packet istransferred to the optical transmission channel 25. The optical packettransferred to the optical transmission channel 24 reaches the repeater3 through the optical transmission channel 8. The optical packettransferred to the optical transmission channel 25 reaches the networkN2 through the optical transmission channel 7. Operation is performed inthe repeaters 3 and 4 in the same manner as in the repeater 2.

As described above, the optical packet in the broadcast transmissionpasses through the repeaters without being subjected to Optical/Electricconversion, and is transferred to all the plurality of opticaltransmission channels connected to all the repeaters, respectively.

Now, a removing process performed by the repeater 1 to break off theoptical packet will be described with reference to FIG. 3.

The optical packet which returns to the repeater 1 serving as the gateto the ring type network 100 is broken off by the repeater 1, preventingthe optical packet from keeping going around the ring type network 100.

The optical packet returns through the optical transmission channel 12to the repeater 1, and when an address recognition circuit 101recognizes that the repeater 1 is the gate repeater to the ring typenetwork 100, a control signal generated based on the recognition resultis output to optical switches 103 and 104. The optical packet enters tothe repeater 1 through the optical transmission channel 12 is split intotwo packets by the optical splitter 102 and these packets are output tothe optical switches 103 and 104, respectively.

The control signal of the address recognition circuit 101 selects anoptical transmission channel 105 in the optical switch 103, and theoptical packet duplicated by the optical splitter 102 is transferred tothe optical transmission channel 105. Meanwhile, an optical transmissionchannel 106 is selected by the optical switch 104, and the opticalpacket duplicated by the optical splitter 102 is transferred to theoptical transmission channel 106. The optical packet transferred to theoptical transmission channel 105 is broken off, and also the opticalpacket transferred to the optical transmission channel 106 is brokenoff. In the above operation, the optical packet which has gone aroundthe ring type network 100 is broken off in the repeater 1 in thebroadcast transmission.

According to the flow of the optical packet described above, the opticalpacket in the broadcast transmission goes around the ring type network100 while the same is kept as an optical signal, and is transferred toall the networks connected to all the repeaters provided within theoptical communication system 1S. Further, since the optical packet doesnot require any electric process of a low processing speed, a broadcasttransmission of the optical packet can be realized at a hightransferring speed without suffering from a transmission delay.

[Multicast]

Using a ring type network as a sample of the communication network, amulticast transmission of the optical packet over an optical packetnetwork will be described with reference to FIGS. 4 to 6.

FIG. 4 is a view illustrating by an example a flow of the optical packet(solid arrows in FIG. 4). In FIG. 4, the network N4 is excluded from thedesignations to which the optical packet is to be transferred. FIG. 5 isa view illustrating a detailed header portion of the optical packet.

As shown in FIG. 5, in the header portion of the optical packet, thereis provided a destination address portion and a source address portionat a position apart by the predetermined number of bits from the leadingbit. The destination address portion and source address portion eachcontain n+1 bits, and the destination address portion is assigned withdestination addresses in units of bit, and the source address portion isalso assigned with source addresses in units of bit.

In the destination address portion, “address 0” indicates whether or nota plurality of destination addresses are included, and “addresses 1 ton” each indicate a destination address. When a value of the bit of“address 0” takes “1”, the multicast transmission or broadcasttransmission (a plurality of designations) is indicated, and when avalue of the bit of “address 0” takes “0”, the unicast transmission(single destination) is indicated. When a value of the bit in “addresses1 to n” of the destination address portion takes “1”, it is indicatedthat destination address has been appointed, and when the value of thebit takes “0”, it is indicated that no designation has been appointed.Further, when a value of any of bits in addresses of the source addressportion takes “1”, an address whose bit takes “1” indicates the sourceaddress.

Assuming that an address 1 indicates the network N1, an address 2 thenetwork N2, an address 3 the network N3, and an address 4 indicates thenetwork N4, FIG. 5 illustrates the optical packet indicating that themulticast transmission of the optical packet is designated with theoriginating source of the network N1 and the destinations of thenetworks N2 and N3. With an address configuration of the optical packetshown in FIG. 5, a number of specified addresses can easily bedesignated in the multicast transmission by setting a value of the bit(address “0”) indicating the multicast transmission to “1” and alsovalues of the bits corresponding to the destination addresses to “1”.The repeaters are not required to read all the bits in the destinationaddress portion and source address portion, but read only the relatedbits. Therefore, the optical packet can be transferred at a highprocessing speed. In the case of the broadcast transmission, it is onlyrequired that all the values of the addresses 1 to n in the destinationaddress portion be set to “1”.

Now, as an example of the multicast transmission, a transferring processfor transferring the optical packet having the header configurationshown in FIG. 5 will be described.

The optical packet generated in the network N1 is transferred to thering type network 100 through the repeater 1. The optical packet istransferred from the repeater 1 to the repeater 2 through the opticaltransmission channel 6. The optical packet is duplicated in the repeater2 and the duplicated optical packets are transferred to the opticaltransmission channels 7 and 8, respectively. The optical packettransferred to the optical transmission channel 7 reaches the networkN2, and meanwhile the optical packet transferred to the opticaltransmission channel 8 reaches the repeater 3. The optical packet isduplicated in the repeater 3 and the duplicated optical packets aretransferred to the optical transmission channels 9 and 10, respectively.The optical packet transferred to the optical transmission channel 9reaches the network N3, and meanwhile the optical packet transferred tothe optical transmission channel 10 reaches the repeater 4.

Since the network N4 is not contained in the destination address portionof the optical packet shown in FIG. 5 (i.e. the value of the bit of theaddress 4 is set to “0”), the repeater 4 transfers the optical packet tothe optical transmission channel 12, but not to the optical transmissionchannel 11. Therefore, the optical packet on the optical transmissionchannel 12 does not reach the network N4. The optical packet has gonearound the ring type network 100 and returned to the repeater 1 servingas the gate repeater to the ring type network 100. When it is confirmedin the repeater 1 that the source address designates the network N1connected to the repeater 1 (i.e. the value of the bit in the sourceaddress portion is set to “1”), the optical packet returning to therepeater 1 is not transferred to the following repeater anymore, butbroken off in the repeater 1.

Referring to FIG. 6, a process is described, which is performed in therepeater 4 to transfer to the following repeater 1 the optical packethaving the header configuration shown in FIG. 5. In the repeater 4connected to the network N4 which has not been designated in thedestination address portion, the optical packet entered from the opticaltransmission channel 10 is not transferred to the network N4 buttransferred only to the optical transmission channel 12 connected to thefollowing repeater 1.

When the optical packet is entered from the optical transmission channel10 to the repeater 4, an address recognition circuit 40 recognizes thatthe network N4 is not included in the destination addresses of theheader portion of the optical packet, and generates a control signalbased on the recognition result. The control signal is output to opticalswitches 42 and 43. The optical switch 42 selects an opticaltransmission channel 44 and the optical switch 43 selects an opticaltransmission channel 45, on the basis of the control signal form theaddress recognition circuit 40. Meanwhile, the optical packet entered tothe repeater 4 is split into two packets by an optical splitter 41, andthe two packets are output to the optical switches 42 and 43,respectively.

In the optical switch 42, the optical packet is transferred to theoptical transmission channel 44, and in the optical switch 43, theoptical packet is transferred to the optical transmission channel 45.Meanwhile, the optical packet transferred the optical transmissionchannel 45 is broken off.

As described above, the optical packet entered to the repeater 4 istransferred only to the repeater 1 without being subjected toOptical/Electric conversion, but not to the network N4 connected to therepeater 4.

According to the flow of the optical packet described above, the opticalpacket in the multicast transmission goes around the ring type network100 while the same is kept as an optical signal, and is transferred onlyto the network designated in the destination address portion. Further,since the optical packet does not require any electric process of a lowprocessing speed in the multicast transmission, the broadcasttransmission of the optical packet can be performed at a high processingspeed without suffering from a transmission delay.

In the repeaters and optical communication system according to theembodiments of the invention, destination addresses are recognized inthe optical packet having a simple address configuration, and theoptical packets split by the optical splitter are transferred to theoptical transmission channels corresponding respectively to therecognized destination addresses. In the above manner, the broadcasttransmission and multicast transmission of a high processing speed arerealized without using conventional electronic processes in therepeaters to electrically process the packet.

More specifically, a processing delay in the repeaters in which theoptical packet does not require Optical/Electric conversion or aprocessing delay in the repeaters in which the optical packet issubjected only to essential electronic processes, is caused only duringoptical transmission of the optical packet in such repeaters. Therefore,the transmission delay is greatly reduced compared with the conventionalrepeater in which the optical packet is subjected to Optical/Electricconversion. Since the transmission delay per repeater is reduced, eventhough a plurality of repeaters are used, the total transmission delayover the whole optical communication system is greatly decreased.

Further, the repeaters according to the invention does not require sucha large scale electronic circuit as employed in the conventionalrepeaters, in which the optical packet is subjected to Optical/Electricconversion. The address configuration of the optical packet forindicating the broadcast transmission or multicast transmission is madesimpler, and therefore a circuit scale of the address recognitioncircuit can be reduced, and the operation speed of the circuit can beincreased, too.

[Duplex Ring Type Network]

Now, a duplex ring type network 300 will be described with reference toFIGS. 7 to 9.

In FIGS. 1 and 4 is shown a single ring type network having the opticaltransmission channels 6, 8, 10 and 12. To enhance redundancy of the ringtype network, the ring type network can be made to a duplex typenetwork, by connecting an additional transmission channel includingoptical transmission channels 13, 14, 15 and 16, as shown in FIG. 7.

Hereafter, a process for transferring an optical packet will bedescribed, which process is performed when the optical transmissionchannel 12 has come down in the ring type network 300 as shown in FIG.8. When a disconnection fault should occur in the optical transmissionchannel 12 in the ring type network 100 as shown in FIG. 1, the opticaltransmission channel is broken down, and communication is interruptedover a portion of the transmission channel where no accidental failureoccurs. In the duplex ring type network 300, when the opticaltransmission channel 12 should be broken down and/or some repeatershould fail to operate properly, only such portion in trouble can beremoved from the transmission channel to allow to a communication overportions operating properly.

In the case that the optical transmission channel 12 should break down,such optical transmission channel 12 is removed from the opticaltransmission channel, and the optical transmission channels 14, 15 and16 are used to establish a ring type network having a new transmissionchannel including a repeater 1 a, optical transmission channel 6,repeater 2 a, optical transmission channel 8, repeater 3 a, opticaltransmission channel 10, repeater 4 a, optical transmission channel 14,repeater 3 a, optical transmission channel 15, repeater 2 a, opticaltransmission channel 16, and repeater 1 a. With use of the new ring typenetwork, the optical transmission channel in trouble is removed, and theoptical transmission channels and repeaters operating properly can beconnected.

FIG. 9 is a view illustrating an interior configuration of repeater 4 a,as one example of the repeaters involved in the ring type network 300.In FIG. 9, like components as those in the repeater 4 (in the ring typenetwork 100) in FIG. 6 are designated by like reference numerals, andtheir description will be omitted.

A duplex control circuit 46 generates a control signal depending on atransmission state of the optical transmission channel connected to therepeater 4 a, and outputs the control signal to optical switches 47 and48. More specifically, detecting a disconnection of the opticaltransmission channel 12, the duplex control circuit 46 outputs thecontrol signal to the optical switch 47, instructing to select a turningtransmission channel for the optical packet.

As a method for detecting a disconnection fault of an opticaltransmission channel and/or a failure of a repeater, it is considered tosend an optical packet for testing to the optical transmission channeland watch an arrival of such optical packet to find out any trouble inthe network. Further, it is possible to detect a disconnection of theoptical transmission channel and/or a failure of the repeater, bywatching an operating state of the ring type network 300 from a separatenetwork, which is prepare for a managing purpose in addition to the ringtype network 300.

In accordance with the control signal from the duplex control circuit46, the optical switch 47 selects a transmission channel for the opticalpacket transferred from the optical transmission channel 44. Meanwhile,in accordance with the control signal from the duplex control circuit46, the optical switch 48 selects a transmission channel for the opticalpacket transferred from the optical transmission channel 13.

An optical coupler 49 couples the optical packet transferred from theoptical switch 47 through the optical transmission channel 51 with theoptical packet entered from the optical switch 48, and transfers thecoupled packet to the optical transmission channel 14. An opticalcoupler 50 couples the optical packet transferred from the repeater 3 athrough the optical transmission channel 10 with the optical packetentered from the optical switch 48 through the optical transmissionchannel 52, and outputs the coupled packet to the address recognitioncircuit 40 and optical splitter 41.

In the case where a disconnection fault occurs in the opticaltransmission channel 12, the duplex control circuit 46 outputs a controlsignal to the optical switch 47, instructing to select a turningtransmission channel for the optical packet. The optical switch 47selects the optical transmission channel 51, and transfers the opticalpacket to the optical transmission channel 51. With the above operation,the optical packet transferred to the repeater 4 a through the opticaltransmission channel 10 is turned in the repeater 4 a and transferred tothe repeater 3 a through the optical transmission channel 14.

As described above, in the case of a disconnection fault in an opticaltransmission channel and/or a failure of a repeater in the duplex ringtype network 300, a transmission channel for the optical packet issecured with the transmission channel operating properly, which allowsthe optical packet to be transferred without failure.

All the disclosure of Japanese Patent Application No. 2005-248945, filedAug. 30, 2005, including the specification, claims, drawings andabstract, is incorporated into a part of the present patent,application.

1. A repeater comprising: a recognizing unit to recognize a destinationaddress of an optical packet from the optical packet which includes thedestination address assigned in unit of bit and a bit indicating whetheror not a plurality of destination addresses are assigned; an opticalsplitting unit to split the optical packet into a plurality of opticalpackets; and selecting units to select transmission channels for thesplit optical packets on the basis of recognition results by therecognizing units, respectively.
 2. The repeater as claimed in claim 1,wherein a plurality of specified addresses can be designated for each ofthe optical packets split by including a combination of bits eachindicating a destination address and a bit indicating that a pluralityof destination addresses are assigned.
 3. An optical communicationsystem comprising a repeater provided in a predetermined network, fortransferring an optical packet, wherein the repeater comprising: arecognizing unit to recognize a destination address of an optical packetfrom the optical packet which includes the destination address assignedin unit of bit and a bit indicating whether or not a plurality ofdestination addresses are assigned; an optical splitting unit to splitthe optical packet into a plurality of optical packets; and selectingunits to select transmission channels for the split optical packets onthe basis of recognition results by the recognizing units, respectively4. The optical communication system as claimed in claim 3, wherein aplurality of specified addresses can be designated for each of theoptical packets split by including a combination of bits each indicatinga destination address and a bit indicating that a plurality ofdestination addresses are assigned.
 5. The optical communication systemas claimed in claim 3, wherein the repeater is provided in a ring typenetwork.
 6. The optical communication system as claimed in claim 4,wherein the repeater is provided in a ring type network.